Phosphoglucomutase activity in developing endosperms --David Pan, Lisa Strelow and Oliver Nelson The developing endosperms of most plants investigated have two phosphoglucomutase (PGM) isozymes. One is the amyloplast enzyme, the other is a cytosolic enzyme, and these isozymes are separable by starch gel electrophoresis. Assaying extracts of inbred maize endosperms 22 days postpollination by starch gel electrophoresis has shown that the majority of the inbreds have only one isozyme present. It has been demonstrated that the isozyme present in all inbreds is the amyloplast form. The inbreds B73, W22, SDP312, W552, A632, H49, B84, A540, B37, N22, and Oh43 have only amyloplast PGM. The inbreds W64A, Mo17, and W570 have both isozymes as does the sweet corn inbred, P39.

The separations by column chromatography (DEAE-cellulose) of the extracts from N22 and Oh43 reveal only a single peak of activity, indicating that the single zone of activity observed on SGE is unlikely to result from two isozymes that migrate to exactly the same zone.

The lack of the cytosolic isozyme has no discernible phenotypic consequence. It appears that this enzyme is completely dispensable for normal endosperm development. It is also possible that the absence of this enzyme is one of the cryptic deficiencies (along with many others) that contribute to the lessened vigor and lower productivity that characterize inbred lines and that is often redressed by crossing to an unrelated inbred line. This hypothesis is testable, and we are proceeding to do so.

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